You should usually get the consent of the other party to record a call, but it isn't always legally required.

Recording your phone calls seems like the sort of thing that you should be allowed to do, right? But then, you'd probably be less cool about someone else recording your calls, and that's what you're doing to the person on the other end of the line when you record your own. For this reason, it's illegal in some parts of the US to record a phone call without the consent of both parties. Each state decides its own rules, and there are also exceptions to getting explicit consent.